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package kea;

/**
 * A stemmer for German words. The algorithm is based on the report
 * "A Fast and Simple Stemming Algorithm for German Words" by Jörg
 * Caumanns (joerg.caumanns@isst.fhg.de).
 *
 * Changed stem() from protected to public.
 * Changed coding for umlaute to unicode.
 *
 * @author    Gerhard Schwarz
 * @version   $Id: GermanStemmer.java,v 1.3 2005/02/03 12:52:20 valyt Exp $
 */
@SuppressWarnings("serial")
public class GermanStemmer extends Stemmer
{
    /**
     * Buffer for the terms while stemming them.
     */
    private StringBuffer sb = new StringBuffer();

    /**
     * Indicates if a term is handled as a noun.
     */
    private boolean uppercase = false;

    /**
     * Amount of characters that are removed with <tt>substitute()</tt> while stemming.
     */
    private int substCount = 0;

    /**
     * Stemms the given term to an unique <tt>discriminator</tt>.
     *
     * @param term  The term that should be stemmed.
     * @return      Discriminator for <tt>term</tt>
     */
    public String stem( String term )
    {
  // Mark a possible noun.
  uppercase = Character.isUpperCase( term.charAt( 0 ) );
  // Use lowercase for medium stemming.
  term = term.toLowerCase();
  if ( !isStemmable( term ) )
      return term;
  // Reset the StringBuffer.
  sb.delete( 0, sb.length() );
  sb.insert( 0, term );
  // Stemming starts here...
  substitute( sb );
  strip( sb );
  optimize( sb );
  resubstitute( sb );
  removeParticleDenotion( sb );
  return sb.toString();
    }

    /**
     * Checks if a term could be stemmed.
     *
     * @return  true if, and only if, the given term consists in letters.
     */
    private boolean isStemmable( String term )
    {
  for ( int c = 0; c < term.length(); c++ ) {
      if ( !Character.isLetter( term.charAt( c ) ) ) return false;
  }
  return true;
    }

    /**
     * suffix stripping (stemming) on the current term. The stripping is reduced
     * to the seven "base" suffixes "e", "s", "n", "t", "em", "er" and * "nd",
     * from which all regular suffixes are build of. The simplification causes
     * some overstemming, and way more irregular stems, but still provides unique.
     * discriminators in the most of those cases.
     * The algorithm is context free, except of the length restrictions.
     */
    private void strip( StringBuffer buffer )
    {
  boolean doMore = true;
  while ( doMore && buffer.length() > 3 ) {
      if ( ( buffer.length() + substCount > 5 ) &&
    buffer.substring( buffer.length() - 2, buffer.length() ).equals( "nd" ) )
      {
    buffer.delete( buffer.length() - 2, buffer.length() );
      }
      else if ( ( buffer.length() + substCount > 4 ) &&
    buffer.substring( buffer.length() - 2, buffer.length() ).equals( "em" ) ) {
    buffer.delete( buffer.length() - 2, buffer.length() );
      }
      else if ( ( buffer.length() + substCount > 4 ) &&
    buffer.substring( buffer.length() - 2, buffer.length() ).equals( "er" ) ) {
    buffer.delete( buffer.length() - 2, buffer.length() );
      }
      else if ( buffer.charAt( buffer.length() - 1 ) == 'e' ) {
    buffer.deleteCharAt( buffer.length() - 1 );
      }
      else if ( buffer.charAt( buffer.length() - 1 ) == 's' ) {
    buffer.deleteCharAt( buffer.length() - 1 );
      }
      else if ( buffer.charAt( buffer.length() - 1 ) == 'n' ) {
    buffer.deleteCharAt( buffer.length() - 1 );
      }
      // "t" occurs only as suffix of verbs.
      else if ( buffer.charAt( buffer.length() - 1 ) == 't' && !uppercase ) {
    buffer.deleteCharAt( buffer.length() - 1 );
      }
      else {
    doMore = false;
      }
  }
    }

    /**
     * Does some optimizations on the term. This optimisations are
     * contextual.
     */
    private void optimize( StringBuffer buffer )
    {
  // Additional step for female plurals of professions and inhabitants.
  if ( buffer.length() > 5 && buffer.substring( buffer.length() - 5, buffer.length() ).equals( "erin*" ) ) {
      buffer.deleteCharAt( buffer.length() -1 );
      strip( buffer );
  }
  // Additional step for irregular plural nouns like "Matrizen -> Matrix".
  if ( buffer.charAt( buffer.length() - 1 ) == ( 'z' ) ) {
      buffer.setCharAt( buffer.length() - 1, 'x' );
  }
    }

    /**
     * Removes a particle denotion ("ge") from a term.
     */
    private void removeParticleDenotion( StringBuffer buffer )
    {
  if ( buffer.length() > 4 ) {
      for ( int c = 0; c < buffer.length() - 3; c++ ) {
    if ( buffer.substring( c, c + 4 ).equals( "gege" ) ) {
        buffer.delete( c, c + 2 );
        return;
    }
      }
  }
    }

    /**
     * Do some substitutions for the term to reduce overstemming:
     *
     * - Substitute Umlauts with their corresponding vowel: äöü -> aou,
     *   "ß" is substituted by "ss"
     * - Substitute a second char of a pair of equal characters with
     *   an asterisk: ?? -> ?*
     * - Substitute some common character combinations with a token:
     *   sch/ch/ei/ie/ig/st -> $/§/%/&/#/!
     */
    private void substitute( StringBuffer buffer )
    {
  substCount = 0;
  for ( int c = 0; c < buffer.length(); c++ ) {
      // Replace the second char of a pair of the equal characters with an asterisk
      if ( c > 0 && buffer.charAt( c ) == buffer.charAt ( c - 1 )  ) {
    buffer.setCharAt( c, '*' );
      }
      // Substitute Umlauts.
      else if ( buffer.charAt( c ) == '\u00E4' ) {
    buffer.setCharAt( c, 'a' );
      }
      else if ( buffer.charAt( c ) == '\u00F6' ) {
    buffer.setCharAt( c, 'o' );
      }
      else if ( buffer.charAt( c ) == '\u00FC' ) {
    buffer.setCharAt( c, 'u' );
      }
      // Take care that at least one character is left left side from the current one
      if ( c < buffer.length() - 1 ) {
    if ( buffer.charAt( c ) == '\u00DF' ) {
        buffer.setCharAt( c, 's' );
        buffer.insert( c + 1, 's' );
        substCount++;
    }
    // Masking several common character combinations with an token
    else if ( ( c < buffer.length() - 2 ) && buffer.charAt( c ) == 's' &&
        buffer.charAt( c + 1 ) == 'c' && buffer.charAt( c + 2 ) == 'h' )
    {
        buffer.setCharAt( c, '$' );
        buffer.delete( c + 1, c + 3 );
        substCount =+ 2;
    }
    else if ( buffer.charAt( c ) == 'c' && buffer.charAt( c + 1 ) == 'h' ) {
        buffer.setCharAt( c, '§' ); 
        buffer.deleteCharAt( c + 1 );
        substCount++;
    }
    else if ( buffer.charAt( c ) == 'e' && buffer.charAt( c + 1 ) == 'i' ) {
        buffer.setCharAt( c, '%' );
        buffer.deleteCharAt( c + 1 );
        substCount++;
    }
    else if ( buffer.charAt( c ) == 'i' && buffer.charAt( c + 1 ) == 'e' ) {
        buffer.setCharAt( c, '&' );
        buffer.deleteCharAt( c + 1 );
        substCount++;
    }
    else if ( buffer.charAt( c ) == 'i' && buffer.charAt( c + 1 ) == 'g' ) {
        buffer.setCharAt( c, '#' );
        buffer.deleteCharAt( c + 1 );
        substCount++;
    }
    else if ( buffer.charAt( c ) == 's' && buffer.charAt( c + 1 ) == 't' ) {
        buffer.setCharAt( c, '!' );
        buffer.deleteCharAt( c + 1 );
        substCount++;
    }
      }
  }
    }

    /**
     * Undoes the changes made by substitute(). That are character pairs and
     * character combinations. Umlauts will remain as their corresponding vowel,
     * as "ß" remains as "ss".
     */
    private void resubstitute( StringBuffer buffer )
    {
  for ( int c = 0; c < buffer.length(); c++ ) {
      if ( buffer.charAt( c ) == '*' ) {
    char x = buffer.charAt( c - 1 );
    buffer.setCharAt( c, x );
      }
      else if ( buffer.charAt( c ) == '$' ) {
    buffer.setCharAt( c, 's' );
    buffer.insert( c + 1, new char[]{'c', 'h'}, 0, 2 );
      }
      else if ( buffer.charAt( c ) == '§' ) {
    buffer.setCharAt( c, 'c' );
    buffer.insert( c + 1, 'h' );
      }
      else if ( buffer.charAt( c ) == '%' ) {
    buffer.setCharAt( c, 'e' );
    buffer.insert( c + 1, 'i' );
      }
      else if ( buffer.charAt( c ) == '&' ) {
    buffer.setCharAt( c, 'i' );
    buffer.insert( c + 1, 'e' );
      }
      else if ( buffer.charAt( c ) == '#' ) {
    buffer.setCharAt( c, 'i' );
    buffer.insert( c + 1, 'g' );
      }
      else if ( buffer.charAt( c ) == '!' ) {
    buffer.setCharAt( c, 's' );
    buffer.insert( c + 1, 't' );
      }
  }
    }
}
